1. Field of the Invention
The present invention relates to standard or reverse flow propellers having individual fan blades whose pitch may be varied and having a locking insert member, that is easily interchangeable, which sets the blade pitch and positively locks the blade to a desired pitch angle.
2. Description of the Related Art
It is often necessary to vary the pitch of the individual blades of a propeller in order to vary the performance characteristics of the propeller and/or to optimize the performance of the propeller relative to the output capabilities of the propeller's power source. Adjustable pitch propellers, using various devices for adjusting the pitch of the blades and locking the blades in a desired pitch position, have been known for a number of years.
For example, U.S. Pat. No. 1,790,844 discloses an adjustable pitch propeller blade having raised ribs extending from a tapered root shank of the blade. Split collars are clamped around the shank to hold each blade to a hub. The split collars have a series of notches on the interior portion of each half of the collar for receiving the ribs on the shank. Different blade pitch positions are achieved by placing the ribs on the shank into different notches in the collars. The blade is clamped to the hub when the two halves of the split collar are bolted together. The blade is retained in the hub axially by an elongated wedge that is inserted through a slot in the blade shank and openings in each half of the collar. This reference provides limited flexibility in blade pitch variation due to the fact that the collars are formed with a discreet number of slots into which the raised rib of the shank can be engaged. In addition, providing a number of slots in the split collars as well as a hole through the shank and the collars for receiving the elongated retaining wedge piece increases manufacturing complexity.
U.S. Pat. No. 3,123,145 discloses variable pitch blades in a hub which includes sockets for receiving the cylindrical shanks of each propeller blade. Both the sockets and the shanks have circumferentially spaced axial grooves formed therein. A key fits within the circumferentially spaced grooves in the root shank and the socket to fix the propeller blade in a desired pitch position. With the key removed, the blade can be rotated within the socket, and by aligning a specific groove in the shank with a specific groove in the socket, a desired pitch angle is achieved. The key is inserted into the aligned grooves to fix the blade in the desired pitch position. In addition, a set screw, extending into the socket perpendicularly to the blade root shank, further fixes the propeller blade in the desired pitch position. The arrangement disclosed in the reference requires complex machining to form the circumferentially spaced grooves in both the blade root shank and the socket. Moreover, pitch variation flexibility is limited due to the fact that there is a fixed number of discreetly spaced grooves formed in the blade root blade shank and the socket.
U.S. Pat. No. 4,600,362 discloses an adjustable pitch fan blade having an interchangeable locking means for fixing the blade in a desired pitch position. The locking means includes key pieces having two spaced projections on one side for engaging two corresponding recesses in the end surface of the blade root shank and two equally spaced projections on the other side of the key piece for engaging two corresponding recess provided in the base of the hub socket. Different key pieces, with varying positions of the two projections for engaging the recesses in the base of the root shank, are interchangeable to allow for different pitch settings of the fan blades. Further, an enlarged shoulder portion of the root shank fits into an enlarged portion of the socket to prevent axial movement of the fan blade when the propeller is assembled.
The key pieces disclosed in the U.S. Pat. No. '362 reference must be individually produced by using an adjustable mold, thereby inhibiting mass production of the key pieces. Furthermore, because the key piece of the reference engages only the end surface of the blade root shank, twisting of the shank is possible, especially where long shank lengths are required for large fan blades. Thus, the arrangement of this reference does not provide sufficient support to prevent pitch-wise rotation of the fan blade. Finally, the key projection, which is recessed into the hub bushing area, can create a potential weak area and potentially limits the assembled propeller diameter, particularly for large diameter propellers.
British Patent No. 713,855 discloses a propeller having a hub portion with a series of radially extending blade seating slots for receiving the root of individual propeller blades. The root shank of the propeller blade has a neck portion of a generally smaller diameter and an enlarged shoulder for engaging an inwardly facing edge of the blade socket. The neck portion has a flatten portion formed on its outer surface. A pitch plate, which slides into the socket perpendicularly to the blade root shank, has a straight edge that abuts against the flat portion of the blade root shank. The pitch of the blade is set by the angle of the straight abutting edge of the pitch plate, and the pitch plate is secured into the hub by a series of screws, thus fixing the blade at the desired pitch angle. The pitch of a blade is varied by substituting a different pitch plate having an abutting edge of a different angular orientation. Due to the fact that the pitch plate contacts a relatively localized portion of the blade root shank, localize stresses on both the blade root shank and the pitch plate, at their respective points of contact, can be extremely high, thus increasing the danger of material failure.
Finally, British Patent No. 1,085,344 discloses an adjustable pitch propeller blade in which the blade root, having an enlarged shoulder at its end, fits into a socket formed to receive the root. A hexagonally shaped key piece fits into a matting opening at the base of the socket. A rectangular projection or key extends from the key piece into a slot in the end of the blade root shank. The key and slot engagement between the key piece and the blade root prevents pitch wise rotation of the blade relative to the hub. Different key pieces having keys of different angular orientations can be used to fix the blades into different positions. The hexagonal shape of the key piece, as well as the hexagonal shape of the portion of the socket that receives the key piece, introduces substantial complexity into the hub fabrication process. In addition, as noted above, because the pitch wise locking of the blade occurs only at the end face of the blade root shank, twisting of the blade root shank is a possibility, especially in applications where a long shank is required.
As is apparent from the above, the need exists for a mechanism, to both set and fix the pitch position of an individual fan blade in a variable pitch propeller, which is easily fabricated, easily interchangeable, and provides positive locking along the entire length of the root shank of the propeller blade to be adjusted.